The present invention relates to radiation-sensitive polymers and to a mixture containing these radiation-sensitive polymers as a binder. The invention also relates to a process for the preparation of the radiation-sensitive polymer binder and to a positive, radiation-sensitive recording material prepared using the radiation-sensitive mixture. The recording material is particularly suitable for the production of photoresists, electronic components and printing plates and for chemical milling.
Positive, radiation-sensitive mixtures have been known for a long time. The use of these mixtures in radiation-sensitive copying materials, such as blueprinting papers, planographic printing plates, colorproof sheets and dry and liquid resists and for chemical milling has frequently been described.
The continuing miniaturization of structures, for example, in chip production, down to the range of less than 1 .mu.m, demands modified lithographic techniques. In order to obtain an image of such fine structures, short wavelength radiation is used, such as high-energy UV light, electron beams and X-rays. The radiation-sensitive mixture must be suited to the shortwave radiation. The demands which must be met by the radiation-sensitive mixture are listed in the article by C. G. Willson "Organic Resist Materials Theory and Chemistry" (Introduction to Microlithography, Theory, Materials, and Processing, edited by L. F. Thompson, C. G. Willson, M. J. Bowden, ACS Symp. Ser. 219: 87 (1983), American Chemical Society, Washington). There is therefore an increased demand for radiation-sensitive mixtures which can be used in the more recent technologies, such as mid-UV or deep-UV lithography, with illumination, for example, by means of Excimer lasers at wavelengths of 305 nm (XeF), 248 nm (KrF) and 193 nm (ArF), electron radiation lithography and X-ray lithography. The mixtures are preferably also sensitive in a broad spectral range and can thus be used in conventional UV lithography.
Two routes have been taken in order to improve the resolution of photoresists. On the one hand, an attempt was made to develop resists based on conventional novolaks/.alpha.-diazocarbonyl compounds for the deep-UV range, which resists have a further reduced solubility in the non-irradiated regions. On the other hand, photoresist systems were developed which are based on the principle of "chemical amplification."
In the presence of e-diazocarbonyl compounds, the solubility of novolaks in alkali is greatly reduced, i.e., the .alpha.-diazocarbonyl compounds act as solubility inhibitors. In addition to the diazonaphthoquinone sulfonic acid esters, 2-diazo-1,3-dicarbonyl compounds, such as 5-diazo-Meldrum's acid, derivatives of 2-diazocyclohexane-1,3-dione and 2-diazocyclopentane-1,3-dione and aliphatic 2-diazo-1,3-dicarbonyl compounds are to be singled out. .alpha.-Phosphoryl-substituted diazocarbonyl compounds and polyfunctional .alpha.-diazo-.beta.-ketoesters are also described as photoactive inhibitors in positive resists, especially those which are radiation-sensitive in the deep-UV range (DUV).
In their article "Positive Excimer Laser Resists Prepared with Aliphatic Diazoketones" (Proc. of the Ellenville Conf. 51 (1988)), H. Sugiyama et al. also propose .alpha.-diazoacetoacetates. Diazocarbonylsulfonyl chlorides are described by Y. Tani et al. [SPIE Proc., Adv. in Resist Techn. and Proc. 1086: 22 (1989)]. Further diazocarbonyl and diazo-1,3-dicarbonyl compounds are given in G. Schwarzkopf [SPIE Proc., Adv. in Resist Techn. and Proc. 920: 51 (1988)]. are given in G. Schwarzkopf (SPIE Proc., Adv. in Resist Techn. and Proc. 920: 51 (1988)).
Upon irradiation, all of these compounds rearrange to form ketene derivatives. These ketene derivatives then react further with residual moisture, which is frequently already present in the resist, to form carboxylic acids. The carboxylic acids, in turn, increase the solubility of the novolaks in aqueous-alkaline developers. However, it has been found that some of the photoactive diazocarbonyl compounds bleed from the resist layer under the relatively high processing temperatures frequently used in practice and the radiation-sensitive mixture thus loses its original activity, so that reproducible results are no longer possible.
It is true that photoactive components are known which have a lower volatility, but these, depending on their structure, show a poorer compatibility in the radiation-sensitive mixture. Especially when drying the radiation-sensitive layers, this has a noticeable adverse effect due to crystallization of the photoactive compound. In addition, these components are frequently sparingly soluble in the conventional solvents. Some of the diazocarbonyl compounds described additionally have the disadvantage that the carbenes formed therefrom upon irradiation do not have a stability in the matrix which is adequate for the desired carboxylic acid formation. This leads to an inadequate difference in solubility between the exposed and unexposed regions during development and thus to an undesirably high degree of stripping in the unexposed regions. An explanation for this phenomenon is proposed by C. G. Willson et al. in SPIE Proc., Adv. in Resist Techn. and Proc. 771: 2 (1987).
.alpha.-Phosphoryl-substituted diazo compounds are not used for resists in practice, since atoms which can be used as doping agents, such as the phosphorus contained in these compounds, have to be strictly excluded in the subsequent processing steps. It is true that derivatives of to image differentiation are poor. Radiation-sensitive recording materials containing the diazocarbonyl compounds described generally have an inadequate photosensitivity, even in combination with highly transparent binders.
Mixtures containing a binder which is insoluble in water and soluble or at least swellable in aqueous-alkaline solutions, a component which forms a strong acid under the action of actinic radiation, and a compound which can be split by acid containing, for example, a C--O--C or C--O--Si bond, are known in principle. See, e.g., DE 23 06 248 (=U.S. Pat. No. 3,779,778).
The compounds forming a strong acid on irradiation which have been used are, in particular, onium salts, such as diazonium, phosphonium, sulfonium and iodonium salts of non-nucleophilic acids, such as HSbF.sub.6, HAsF.sub.6 or HPF.sub.6 (J. V. Crivello, Polym. Eng. Sci. 23: 953 (1983)). In addition, halogen compounds, particularly trichloromethyltriazine derivatives or trichloromethyloxadiazole derivatives, o-quinonediazidesulfonyl chlorides, o-quinonediazide-4-sulfonic acid esters, organometallic/organohalogen combinations, bis(sulfonyl)diazomethanes, sulfonylcarbonyldiazomethanes (DE 39 30 087) and nitrobenzyltosylates (F. M. Houlihan et al., SPIE Proc., Adv. in Resist Techn. and Proc. 920:67 (1988)) have been recommended.
The strong acid formed upon irradiation of the materials described above splits the C--O--C or C--O--Si bonds of the acid-labile compounds. As a result, the exposed regions of the photosensitive layers become more soluble in an aqueous-alkaline developer. If shortwave radiation is used for irradiation, this demands new binders which are highly transparent at these wavelengths. However, radiation-sensitive layers composed of mixtures comprising such a highly transparent, radiation-insensitive binder, an acid-labile compound having at least one C--O--C or C--O--Si bond which can be split by acid, and a compound which forms a strong acid on irradiation have a solubility in the developer in the non-irradiated regions that is too high. This is reflected in an unacceptable dark-erosion. The consequence of this is an inadequate edge profile and a reduced resolution. Overall, the systems described above based on the principle of "chemical amplification" do have an exceptionally high photosensitivity (50 mJ/cm.sup.2 and less), but an unsatisfactory resolution for structures in the range of less than 0.5 .mu.m.
Radiation-sensitive mixtures, which contain radiation-sensitive polymers, have already been described for a number of applications. Condensation products of novolak resins with orthoquinonediazide compounds (see, e.g., DE 30 09 873=U.S. Pat. No. 4,308,368, DE 30 28 308, EP 242,143) are particularly important. However, as a result of the novolak constituent, these radiation-sensitive polymers have absorption characteristics which make them unsuitable for exposure in the DUV range.
More transparent, radiation-sensitive polymers can be prepared by a condensation reaction of hydroxyl group-containing polymers, such as poly(4-hydroxystyrene) or copolymers of pyrogallol with ketones, and polyacrylates with 2,1-diazonaphthoquinone-5- and/or -4-sulfonic acid chlorides. The hydroxyl group-containing polymers have, however, an extremely high solubility in standard developers, which is reduced only after the predominant proportion of the free hydroxyl groups has reacted. This results in a high proportion of diazonaphthoquinone units. This leads to unacceptable optical characteristics especially at 248 nm. Examples of mixtures containing such polymers are given in DE 20 28 903 (=U.S. Pat. No. 3,837,860), DE 23 52 139, DE 24 61 912 (=GB 1,494,640) and EP 307,828.
Radiation-sensitive polymers having a diazocarbonyl group as a photosensitive component are given in JP 01-106,037. The radiation-sensitive unit is bonded to the alkyl chain of a 4-alkyl-substituted polystyrene. The polymers are characterized by low thermal stability and an inadequate sensitivity to radiation. 2-Diazo-1,3-dicarbonyl units, bonded to conventional novolak resins, have, as already discussed in detail above, a low transparency in the range of shortwave radiation and unsatisfactory bleed characteristics. Radiation-sensitive recording materials containing polymers having 2-diazo-1,3-dicarbonyl groups as a radiation-sensitive structural element, in particular those containing maleimide/olefin copolymers, are disclosed in U.S. Pat. No. 4,910,123. The resist materials prepared with these polymers have, however, a radiation sensitivity of only about 50 mJ/cm.sup.2.